nixos: show the manual in system's /share/doc (close #9928)

Changed files
+1 -1
nixos
modules
services
+1 -1
nixos/modules/services/misc/nixos-manual.nix
···
system.build.manual = manual;
-
environment.systemPackages = [ manual.manpages help ];
boot.extraTTYs = mkIf cfg.showManual ["tty${cfg.ttyNumber}"];
···
system.build.manual = manual;
+
environment.systemPackages = [ manual.manpages manual.manual help ];
boot.extraTTYs = mkIf cfg.showManual ["tty${cfg.ttyNumber}"];